Typically, pressure and drainage of fluids within the middle ear are influenced by the Eustachian tube and gas regulation in the middle ear cavity. When this regulation is not functioning properly, the pressure within the middle ear tends to drop, interfering with the drainage of the fluid by the Eustachian tube. The results of this pathology are accumulation of fluid, middle ear infections (mainly in infants), and sometimes retraction of the eardrum. All these conditions cause loss of hearing, infections endangering the ear, severe pain mostly in infants, destruction of major structures of the middle ear and other complications.
In order to ventilate the middle ear and enable drainage, ear tubes were found to be the best efficient solution, and are advantageous compared to other medical methods. However, their insertion needs minor surgical procedure, frequently under general anesthesia (mainly in children). Other disadvantages of tubes are damage to the eardrum and lack of control of the stay of the rigid type of tubes.
The tube provides gas supply to the middle ear and drains pus when present. Preventing the accumulation of fluid reduces the risk for infection.
Tubes with small internal diameter (I. D.) of less than 1.0 mm tend to clog with secretions. The long narrow shaft of the long standing T-tubes is unsuitable for draining pus. The wider I. D. (>1.2 mm) of the rigid tubes is better, but these kinds of tubes have other disadvantages, such as short-term longevity and difficult extrusion.
To install a tube, a small incision is made in the eardrum and the tube is inserted therethrough.
There are various types of ear tubes. They can be divided into two major groups: rigid (or semi-rigid) and flexible.
The rigid types basically with the form of a bobbin, first designed by Armstrong (1954), are available in many varieties. They are made of polyethylene, silicone, metals and other inert materials and produced by many manufacturers. They are formed as a shank with a trailing flange. Retention of this kind of tube is unpredictable. It tends to fall out of the ear after about a year, and there is no way to ensure its retention. It may fall out within days or last for years.
The flexible type of ear tubes, commonly called a T-tube on account of its shape (first designed by Goode), stays longer and is easy to remove, but needs repeated cleanings by a physician and has up to a 20% rate of causing permanent perforation in the eardrum. The flange of the T-tube unfolds at an angle of 90° to its axis. The flange creates pressure on the eardrum in the area close to its insert and erodes it, causing perforation, frequently permanent.
Sometimes T-tubes tend to shift and align themselves across the ear canal or block the tube, thereby making the checking thereof or the access to its lumen difficult.
Another disadvantage of the T-tubes is the difficulty of insertion. This procedure takes longer and is more painful, and needs general anesthesia in children and even in some of adult patients.
Both the rigid and the T-type tubes cause thinning of the eardrum at the site of the insertion in more than 20% of the cases in addition to the tendency to perforate the eardrum. This is also a result of the interaction between the edges of the tube and the rim of the eardrum-perforation in which it sits.
In thin eardrums neither tube is retained, and falls out shortly after insertion. In this condition there is a high probability for the occurrence of a permanent perforation. The T-tube does provide some support, though only for a limited thinned area.
In cases where the eardrum is very thin and retracted on the medial wall of the middle ear cavity, adhesion between the eardrum and the medial wall occurs, causing loss of hearing and destruction of principal structures of the middle ear. This may lead to a destructive process inside the middle ear called cholesteatoma.
All the tubes have their contact with the eardrum at the rim of the perforation. For example, the ‘bobbin’ type is described e.g. in U.S. Pat. No. 4,174,716, and U.S. Pat. No. 4,468,218, the ‘T’ type is described in U.S. Pat. No. 4,695,275 and US2004/0077989, and a V-shaped type is described in U.S. Pat. No. 4,808,171. None of said patents or applications, however, teach or suggest a contact area which is distant from the rim of the perforation. Since the tube is slowly pulled away from the eardrum by the external layer of the epithelium advancing over its surface, the point of maximal pressure on the eardrum is at the anchoring collar of the tube, at the rim of the perforation. At this point exists the highest pressure on the tissue. This problem is found in all the tubes and is the cause for perforations and granulation tissue.
There is a need for an improved ear tube that can be easily inserted, easily removed according to the physician decision, suitable for draining pus from infected middle ear (acute otitis media) or ventilating poorly ventilated ears (otitis media with effusion), quickly and easily inserted (preferably as an outpatient procedure), stays in place as long as required, does not tend to cause permanent perforations in the eardrum, stays perpendicular to the ear drum and can readily been cleared if it becomes obstructed, supports thin parts of the eardrum (preventing adhesions), can be anchored even in a thin eardrum, and provides for good visibility during the insertion procedure for a better and more accurate placing.